The present invention relates to the automated manufacturing of fiber optic couplers.
Overclad fiber optic couplers are a type of fused fiber coupler wherein the coupling region is enclosed within a layer of matrix glass which strengthens and encloses the coupling region. To form an overclad fiber optic coupler, the stripped portions of a plurality of fibers are inserted into the bore of a glass capillary tube to form a coupler preform. The tube bore has enlarged funnel-shaped end portions that facilitate the insertion of optical fibers. The midregion of the coupler preform is heated to collapse the tube onto the fibers; the coupler preform is then stretched until the desired coupling characteristics are obtained. Various types of overclad fiber optic couplers and methods of making such couplers are disclosed in U.S. Pat. Nos. 35,138, 4,902,324, 4,979,972, 5,011,251, 5,251,276 and 5,268,014. The methods disclosed in these patents include many manual operations.
In accordance with conventional practice, the manually operated fiber draw apparatus has been oriented such that the tube is vertically positioned. The fibers have been inserted into the tube either on-line or off-line. The off-line fiber insertion process (U.S. Pat. No. 4,902,324) requires that the fibers be tacked to the tube to prevent the fibers from moving with respect to the tube during the step of transferring the coupler preform to the coupler draw apparatus. The tacking glue can cause problems in the resultant coupler. Moreover, the off-line method requires additional steps to transfer the tube to the draw apparatus. The previously employed methods of inserting fibers into the tube either on-line or off-line have been tedious, time consuming processes that are sensitive to the manipulations of each operator. This can affect process reproducibility and thus the optical characteristics of the couplers.
Optical fibers must be prepared prior to inserting them into the tube. The protective coating is removed from the portion of the fiber that is to be positioned within the tube during the coupler drawing operation. If the bare portion of the optical fiber is at the end of the fiber, it is preferred that it be provided with a low reflectance termination. An off-line process for forming such a termination is disclosed in U.S. Pat. Nos. 4,979,972 and 5,011,251. Also, the bare fiber portions must be free from contamination. Manual performance of these fiber preparation steps is time consuming and is subject to the particular manipulations of the operator.
During the stripping of coating from the fibers, the termination of fibers, and the insertion of the stripped portions of fibers in the overclad tube, the fibers must be precisely positioned.
In the manual technique for making overclad fiber optic couplers, the fibers were threaded through the glass tube, the tube was clamped into the draw apparatus. Thereafter, the fiber pigtails extending from the glass tube were inserted through vacuum attachments which were then affixed to the ends of the tubes. Such vacuum attachments are unsuitable for an automated apparatus for manufacturing fiber optic couplers. A preferred heat source for forming overclad fiber optic couplers has been a ring burner that directs flames inwardly toward the glass tube. Heretofore, the glass tube has been manually inserted through the ring burner, and its ends were then clamped. Such a burner is not suitable for use in a fully automated apparatus.
In an automated fiber optic coupler manufacturing process, couplers can be made at a greater rate than they could be made by the aforementioned manual process. The heat source must be activated during the stretching of each coupler. This tends to cause the temperature of certain parts of the apparatus near the heat source to become hotter than they did in the manual process. Some of those apparatus parts and the coupler epoxy can be damaged by the higher temperature or can be dimensionally altered whereby process reproducibility is affected. Precautions must be taken to avoid such heat induced damage.
After the coupler has been formed by stretching the overclad tube and fibers, a glue such as an ultraviolet (UV) curable epoxy is inserted into the uncollapsed ends of the tube bore to provide the fibers with pull strength. Conventional off-line epoxy applying and curing techniques are not suitable for use in a fully automated coupler making process since they do not result in the application of a sufficient amount of epoxy into both ends of the bore, and since they are time consuming processes.
In view of the above mentioned disadvantages of conventional methods of manufacturing fiber optic couplers, it is an object of the present invention to provide an apparatus and method of precisely and automatically manufacturing a fiber optic coupler having predetermined coupling characteristics. Another object is to provide a coupler manufacturing apparatus and method in which opportunities for operator caused process inconsistencies are minimized or eliminated.
The present invention relates to various apparatus components and method steps for making fiber optic couplers. Utilization of the invention in its entirety results in the completely automated production of a fiber optic coupler. However, portions of the inventive method and apparatus can be used to improve conventional methods of the type described above. Whereas the present invention is described in conjunction with the manufacture of overclad fiber optic couplers, certain of the apparatus components can be employed in the manufacture of fused biconic tapered couplers of the type wherein two or more fibers are fused together and elongated, without the use of an outer protective glass tube.
The present invention relates to an apparatus for the automated manufacture of fiber optic couplers. Fiber insertion means including adjacently disposed fiber guide tubes insert optical fibers into a glass tube. The fiber guide tubes have fiber input and fiber output ends, the output ends being movable longitudinally with respect to the bore of the glass tube. Means is provided for delivering the optical fibers to the input ends of the fiber guide tubes, with the first ends of the fibers passing through the fiber guide tubes and being deliverable from and retractable into the second ends of the guide tubes. Means is provided for sequentially tensioning each of the optical fibers and for stripping protective coating from the tensioned length of each of the fibers. The apparatus includes coupler draw means that is provided with upper and lower chucks for securing the glass tube at its end regions. The chucks are movable in opposite directions. First and second vacuum seal means evacuate the bore and maintain closed the ends of the glass tube after the stripped regions of the fibers have been inserted into the bore. Heating means heats the glass tube. Programmable control means control the operation of the apparatus.
The coupler draw means can include an upper clamping bar that engages an upper V-groove provided in the upper chuck and a lower clamping bar that engages a lower V-groove provided in the lower chuck; the clamping bars apply a repeatable level of force to the glass tube to secure it in the V-grooves.
The apparatus can include transfer means for transfering a glass tube from a storage magazine to the chucks. This apparatus can include a holding member provided with a groove, delivery means for delivering a tube from the magazine to the groove, and clamping means for gripping a tube. Means can be included for accurately locating the glass tube in the groove. When it is in a first position, the clamping means engages the glass tube held in the groove. The clamping means then moves to a second position and places the glass tube in the chucks of the coupler draw means.
The means for delivering the optical fibers to the fiber insertion means can include at least two optical fiber supplies, and a fiber feed mechanism for paying out a predetermined length of each of the optical fibers from the sources to the fiber insertion means. The programmable control means controls the fiber delivering means, whereby it measures the optical fibers to the predetermined lengths. That is, precise amounts of fiber are advanced from or retracted into the fiber delivering means.
The fiber feed mechanism can include input guide tubes for receiving the optical fibers from the reels, and output guide tubes that are connected to the fiber guide tubes of the fiber insertion means. A fiber extending between the input and output guide tubes is disposed between an idler roller and a motor driven roller. When the idler roller engages the motor driven roller, the fiber is delivered to or retracted from the output guide tube. Fittings are connected to the output guide tubes for introducing a gas therein for reducing friction between the fiber guide tubes and the optical fibers.
A lubricant dispensing tube can be disposed adjacent the fiber feed tubes and extend a distance beyond the ends of the feed tubes to lubricate the bore of the glass tube as the optical fibers are inserted therethrough.
The means for sequentially tensioning each of the optical fibers can include an upper and a lower stripping clamp between which a length of each of the optical fibers is sequentially clamped and tensioned, and the means for stripping the protective coating from the optical fibers can include a stripping nozzle movable transversely and rotatably with respect to the length of optical fiber that is tensioned between the stripping clamps. The stripping nozzle emits a jet of hot inert gas to strip the protective coating away from the length of fiber as the nozzle moves along the coated fiber.
The apparatus can include means for providing a low reflectance termination on an optical fiber. A ball termination torch is vertically and horizontally movable with respect to the optical fibers tensioned between the stripping clamps. After the torch severs the fiber, the stripping clamps retracting in opposite directions.
Bottom clamp means can be provided for clamping one or more of the optical fibers that extend from that end of the glass tube remote from the fiber insertion means.
The heating means is preferably located away from the chucks. After the stripped portions of the fibers are positioned in the tube bore, the heating means moves to a position adjacent the chucks. The heating means can be formed of two sections that close and surround the glass tube.
The upper and lower chucks partially shield the glass tube from the heating means, and in addition, the chucks are maintained at a controlled temperature by water-cooling to enhance process reproducibility.
After the midregion of the glass tube has been heated, the chucks are moved in opposite directions to stretch the tube. The means for delivering fibers and the upper chucks are preferably mounted on a first movable stage, and the lower chucks and the bottom clamp are preferably mounted on a second movable stage, whereby the means for delivering fibers and the bottom clamp move in opposite directions as the tube is stretched.
The apparatus can include dispensing means for dispensing glue into the bore of the glass tube, after a coupler has been formed and means for curing the glue after the glue has been dispensed into the bore. The means for curing the glue can comprise a UV light source sequentially positioned at each of the ends of the glass tube.
A further embodiment includes first and second fiber insertion means, each capable of inserting at least two optical fibers into a glass tube. The first and second fiber insertion means are each provided with at least two adjacent fiber guide tubes that are movable longitudinally with respect to the tube bore. Means are provided for moving the first and second fiber insertion means laterally with respect to the bore. This apparatus is especially useful when used in conjunction with first and second means for forming stripped regions in each of the optical fibers. The first fiber insertion means can be disposed adjacent the glass tube when the second fiber insertion means is disposed adjacent the second means for forming stripped regions.
Yet another embodiment pertains to an apparatus for modifying an optical fiber. It includes means for delivering an optical fiber to a fiber guide tube such that the fiber can move out of and into the fiber guide tube. Means is provided for moving the fiber guide tube from one to another of a plurality of work stations. This apparatus can include means for moving the fiber guide tube toward and away from the first work station.
The invention also pertains to a method of automatically manufacturing a fiber optic coupler. A glass tube is placed into a coupler draw means where its end regions are gripped by upper and lower chucks. At least two optical fibers are delivered to a fiber insertion means. While a length of each of the optical fibers is tensioned between upper and lower stripping clamps, protective coating is stripped from each of the optical fibers, and the fibers are then inserted through the glass tube such that the stripped regions extend within the bore. The ends of the glass tube are evacuated, and the tube is heated. The end regions of the glass tube are drawn in opposite directions to form a tapered coupling region. The steps of the method are controlled by programmable control means.
The glass tube can be gripped in the coupler draw means by securing one of the tube end regions between an upper chuck V-groove and upper clamping bar, and securing the other end region between a lower chuck V-groove and a lower clamping bar, the upper and lower clamping bars applying a force to the glass tube to secure the glass tube in the upper and lower V-grooves. The upper and lower chucks can be maintained at a controlled temperature to improve process reproducibility.
The glass tube can be placed into the coupler draw means by automatically transferring the glass tube from a glass tube storage magazine to the draw means.
The optical fibers can be delivered to the fiber insertion means by paying out each of the optical fibers from fiber sources to fiber guide tubes of the fiber insertion means. The fiber guide tubes can move longitudinally with respect to the bore of the glass tube. A gas can be introduced into the fiber guide tubes to reduce friction between the fibers and the tubes and to remove debris from the fibers entering the guide tubes.
A stripped region can be formed on a fiber by positioning the fiber guide tubes above a lower stripping clamp, and delivering a length of an optical fiber is delivered through one of the fiber guide tubes to the lower stripping clamp which grips the fiber at a first location. The guide tubes are moved upwardly so that the upper stripping clamp can grip the fiber at a second location. The fiber is then tensioned between the first and second locations. A jet of hot inert gas is directed onto a predetermined region of the tensioned fiber to heat it and strip coating therefrom.
A low reflectance termination can be provided on an optical fiber prior to inserting it through the glass tube. The fiber is tensioned between two spaced points. A ball termination torch is moved from a given location in a given direction with respect to the optical fiber such that a portion of the flame severs the fiber into two pieces each having a tapered end. At least one of the tapered ends is retracted away from the other of the tapered ends. The torch continues to move such that the flame heats the retracted tapered end to cause it to become shortened and rounded.
A lubricant is preferably dispensed into the glass tube when the optical fibers are inserted therethrough. This can be done by disposing a dispensing tube adjacent the fiber guide tubes, and dispensing the lubricant therefrom.
The method can further include dispensing glue into the uncollapsed ends of the bore of the glass tube after the tapered coupling region has been formed. The glue can initially be cured by directing UV light beams at each of the end regions of the glass tube while the glue is being applied to the ends of the bore, the flow of the glue stopping when it contacts the light beams. The glue can be further cured by sequentially positioning a UV light source at each of the end regions of the glass tube after the glue has been dispensed into the bore.